The calcaneus and talus bone which make up the sub-talor joint of the ankle, bear the entire body weight. This sub-talor joint, as well as the tibia, fibula and talus joint line combine with strong ligaments to make up the ankle's principle means for joint stability. The tibia and fibula end distally in two easily felt prominences called the malleoli on either side of the ankle. The talus resembles a saddle that the distal tibia and fibula rest on and move over. There are four major ligaments that attached to these bones of the ankle. On the medial side (inside) there are the deltoid ligaments. On the lateral side (outside) there are the calcaneo-fibular ligament, the anterior talo-fibular ligament and the posterior talo-fibular ligament. All of these major ligaments attach either to the calcaneus or talus bones.
In considering the causation of skeletal abnormalities and ankle sprains, it must be remembered that the calcaneus and talus are the weight-bearing bones in the ankle. If the heel is turned in, body weight is shifted to the outside and a stretch is placed on the lateral ligaments. If the heel is turned out, force is placed on the medial ligaments. Therefore, it is the stability of the calcaneus that controls the stability of the ankle joint. Similarly, any structural foot or leg deformity which causes the calcaneus to shift from its vertical position will favor ankle sprains.
The prior art ankle brace described in Johnson, Jr., U.S. Pat. No. 4,280,489 relates to an orthopedic apparatus for use in connection with the lower extremity and for immobilizing the ankle against inversion or eversion while permitting planer-flexion and dorsi-flexion. Grim, U.S. Pat. No. 4,844,094 and Brewer, U.S. Pat. No. 4,966,134, both disclose a U-shaped stirrup having a base portion and a pair of opposed sidewalls shells similar to that of Johnson, Jr. ('489).
In all three of the aforementioned patents, the pair of opposed sidewall shells follow the line of the tibia and fibula past the malleoli and then become narrower the closer they get to the bottom of the leg and foot, leaving the calcaneus exposed. This in turn leaves the sub-talor joint unprotected. If the sub-talor joint and the calcaneus are not stabilized, then a sprain involving the calcaneo-fibular ligament or the deltoid ligament cannot heal correctly. The deltoid also attaches to the calcaneus, or in the case of preventative use, the arrangement would be similar to wearing no brace at all.
Each of U.S. Pat. Nos. 4,280,489, 4,844,094 and 4,966,134 relate to an ankle brace or protector to limit inversion and eversion, with the only apparent difference between the apparatus described being what is interiorly disposed therein (i.e., air, gel, a pad with higher surface friction space, or the like). These references disclose ankle orthoses each of which simply act as a splint, somewhat limiting inversion and eversion, but falling far short of real total ankle stability. No attempt is made in the prior art references to control the sub-talor joint which includes the calcaneus. Without controlling the calcaneus and sub-talor joint and their ligaments, ankle braces described in the prior art are cannot provide the ankle stability obtained with the present invention.
Most of the major ligaments in the ankle attach to the calcaneus at some point. With this attachment in mind and the fact that the total body weight is placed on the heel bone, when the ankle inverts or everts, this does not result in inversion or eversion, which the prior art is trying to limit. However, the prior art does not anticipate rear foot valgus or varus stress. It is critical that an ankle brace control the calcaneus as well as the tibia, fibula and talus. A need therefore exists for a complete ankle orthosis which not only limits standard inversion and eversion, but stabilizes rear foot stresses by immobilizing the calcaneus. This is a principle object of the present invention.
It is realized by the present invention that ankle stability is gained not just by limiting inversion and eversion, but by reducing all abnormal torques in the ankle that may be twisting or pulling the foot toward a potential sprain. While planar-flexion and dorsi-flexion are critical to a normal range of motion (walker, running, etc.), anterior excursion and some posterior excursion at the joint line must also be limited to provide yet more stability. Excursion occurs when the talus glides forward or backward at the joint, due to ligament lesions, principally the anterior talo-fibular ligament.
A biomechanical workup is considered in determining the cause of frequent sprains to the ankle. The deforming force must be neutralized with the use of orthotic devices with a rearfoot post to properly balance the foot. In this way the chance of future sprains should be reduced. Ankles with extremely flexible and elastic joints also have a tendency toward ankle sprain. Once an ankle is sprained, it is never as strong as before the injury. Therefore, the use of an orthotic device for the prevention of future recurrent ankle sprains is most necessary in an active ankle.
A rigid orthosis is necessary to prevent the heel from eversion. An orthotic device that grasps the heel bone and, with the addition of a rear platform or post, only allows the heel to move an amount necessary for normal function also is desired.